object shape change when i duplicate object in a curve
Try using dupliverts instead of the array modifier. The manual page on Dupliverts explains it well:


  First, in Object Mode, select the base object and Shift-RMB to add the
  circle to the selection (order is very important here), and Ctrl-P to
  parent the base object to the circle. Now, the circle is the parent of
  the monkey; if you move the circle, the monkey will follow it.
  
  With only the circle selected, enable Duplication vertices in the
  Object panel ‣ Duplication ‣ Vertices. A monkey head should be placed
  at every vertex of the circle.




Be sure to go to the bottom left of the manual page and use the pop-up menu to switch from English to your language, if it is on the list.